docs: def efficiency(self):
          """Calculate :ref:`pysynphot-formula-qtlam`.
  
          Returns
          -------
          ans : float
              Bandpass dimensionless efficiency.
  
          """
          mywaveunits = self.waveunits.name
          self.convert('angstroms')
  
          wave = self.wave
          thru = self.throughput
          self.convert(mywaveunits)
  
          ans = self.trapezoidIntegration(wave, thru/wave)
          return ans